Experts believe signs of life beyond the solar system could be detected within two to three year, after rethinking the types of planets that might be habitable.
Researchers have mainly focused on planets with similar sizes, mass, temperatures, and atmospheric composition to Earth. Astronomers at the University of Cambridge believe that there are more possibilities. Recent work suggests that a mini-Neptune with a radius twice as large as Earth's and a mass eight times greater than Earth may also be habitable.
The new class of habitable planets has been identified as hycean exoplanets. They are hot, ocean-covered, and have hydrogen-rich atmospheres. These planets are more common and easier to observe than Earth-like ones. K2-18b is the mini-Neptune. There could be many others.
According to Dr Nikku Madhusudhan of the University of Cambridge, Hyceans are water worlds that have hydrogen-rich atmospheres. He suggested that focusing on Hyceans could help accelerate efforts to discover life beyond Earth.
He said that we believe that in two to three years, there may be the first detection of biosignature if these planets are home to life. The James Webb space telescope, due to launch in November, could also aid this search.
Madhusudhan stated that Earth-like planets are smaller than sun-like stars, which makes it harder to detect signs of life.
However, hyceans can have a radius more than twice that of Earth, for a planet with 10 times the mass. They are also significantly hotter with the average atmospheric temperature reaching nearly 200C.
Madhusudhan stated that larger planets are more common than Earth-sized ones and easier to find.
Furthermore, the composition of hycean moons makes it possible to search for more molecules that could indicate the existence of life.
The Astrophysical Journal team stated that hycean-planets are defined by a hydrogen rich atmosphere, a rocky core accounting for at least 10% and a water layer accounting up to 90%.
The team has discovered that life may be possible even on the dark side of some planets. They are located close to their star, and they are tidally locked. This means that the same side is always in the sun and could be too hot to make it habitable.
According to the team, any life found on hyceans must be aquatic since planets are covered by water. Madhusudhan isn't sure what kind of life such life might take.
He said that microbial life should only be considered possible at a minimum. This is how life began on Earth.
Professor Beth Biller from the Institute of Astronomy, Edinburgh University, is a specialist in exoplanets and she welcomed the research. She said that there is so much diversity among exoplanets found to date, it makes sense to also study non-Earth-like worlds that could possibly host life.
Biller said that it may be difficult to find biosignatures on hycean-planets. It is already difficult to find biosignatures of Earth twins. They rely on the detection of a mixture of biosignature gases that should not exist in an equilibrium state. Although this is possible for hycean worlds, it is not possible to exclude false positives.
Biller stated that data from both types of planets would be required from a large number of bodies in order to determine which ones may be habitable.
She said that [the James Webb space telescope] will provide some interesting spectra on hycean worlds over the next few years. However, it is difficult to know if such spectra can be conclusive.
